Conductive ball and electronic device

ABSTRACT

A conductive ball includes a copper ball, a nickel layer formed with being patterned on an outer surface of the copper ball, and a tin-based solder covering each outer surface of the copper ball and the nickel layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2017-131925 filed on Jul. 5, 2017, the entire content of which is incorporated herein by reference.

BACKGROUND Technical Field

The present disclosure relates to a conductive ball and an electronic device.

Related Art

In the related art, an electronic device having a structure in which an upper wiring substrate is connected to a lower wiring substrate via conductive balls has been known. The conductive ball is formed by covering a solder on an outer surface of a copper ball.

-   Patent Document 1: JP-A-2010-99736

As described later in paragraphs of preliminary matters, there is an electronic device in which a connection pad of a lower wiring substrate and a connection pad of an upper wiring substrate are interconnected by a conductive ball. The conductive ball is formed by sequentially covering a Ni layer and a Sn/Ag solder on an outer surface of a Cu ball.

In the electronic device, when subjecting the conductive ball to reflow heating so as to connect to each connection pad, a brittle Ni₃Sn₄ layer, which is thermally unstable, is formed between the connection pad and the Sn/Ag solder and between the Ni layer and the Sn/Ag solder of the conductive ball.

For this reason, when heat is applied, the Ni₃Sn₄ layer grows, so that a crack is generated or Ni moves by electromigration and a void is thus generated.

SUMMARY

Exemplary embodiments of the present invention provide a conductive ball having a novel structure capable of reliably connecting a lower electronic member and an upper electronic member, and an electronic device.

A conductive ball according to an exemplary embodiment, comprises:

a copper ball;

a nickel layer formed with being patterned on an outer surface of the copper ball; and

a tin-based solder covering each outer surface of the copper ball and the nickel layer.

An electronic device according to an exemplary embodiment, comprises:

a lower electronic member having a first connection pad;

an upper electronic member arranged above the lower electronic member and having a second connection pad; and

a conductive ball configured to interconnect the first connection pad of the lower electronic member and the second connection pad of the upper electronic member,

wherein the conductive ball comprises:

a copper ball,

a nickel layer formed with being patterned on an outer surface of the copper ball, and

a tin-based solder covering each outer surface of the copper ball and the nickel layer.

A manufacturing method of a conductive ball according to an exemplary embodiment, the manufacturing method comprises:

preparing a copper ball;

patterning and forming a nickel layer on an outer surface of the copper ball; and

forming a tin-based solder covering each outer surface of the copper ball and the nickel layer.

A manufacturing method of an electronic device according to an exemplary embodiment, the manufacturing method comprises:

preparing a lower electronic member an upper electronic member and a conductive ball, the lower electronic member having a first connection pad, the upper electronic member having a second connection pad, the conductive ball comprising a copper ball, a nickel layer formed with being patterned on an outer surface of the copper ball, and a tin-based solder covering each outer surface of the copper ball and the nickel layer; and

interconnecting the first connection pad of the lower electronic member and the second connection pad of the upper electronic member by reflow heating the tin-based solder of the conductive ball.

According to the present disclosure, in the conductive ball, the nickel layer is formed with being patterned on the outer surface of the copper ball. Also, the tin-based solder covers each outer surface of the copper ball and the nickel layer. In this way, portions of the outer surface of the copper ball are exposed from the pattern of the nickel layer and are in contact with the tin-based solder.

The connection pad of the lower electronic member and the connection pad of the upper electronic member are interconnected by the conductive ball. When the conductive ball is reflow-heated, copper in the copper ball is diffused from opening regions of the nickel layer to the tin-based solder.

Thereby, the (Cu, Ni)₆Sn₅ layer, which is an intermetallic compound, is formed between the nickel layer and the tin-based solder of the conductive ball and between each connection pad of the upper and lower electronic members and the tin-based solder.

Since the (Cu, Ni)₆Sn₅ layer has a thermally stable property and the crystal growth does not occur therein even when heat is applied thereto, a crack is prevented from being generated in a connection part. Also, since the (Cu, Ni)₆Sn₅ layer functions as a barrier layer having high reliability of electromigration countermeasures, a void is prevented from being generated in the connection part.

Accordingly, it is possible to improve the connection reliability by the conductive ball between the lower electronic member and the upper electronic member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view depicting a conductive ball relating to preliminary matters.

FIG. 2 is a sectional view depicting a lower wiring substrate and an upper wiring substrate, which are to be connected by the conductive ball of FIG. 1.

FIG. 3 is a sectional view depicting an aspect in which the upper wiring substrate is connected to the lower wiring substrate by the conductive ball relating to the preliminary matters (1 thereof).

FIG. 4 is a sectional view depicting the aspect in which the upper wiring substrate is connected to the lower wiring substrate by the conductive ball relating to the preliminary matters (2 thereof).

FIG. 5A is a sectional view depicting a conductive ball of an exemplary embodiment.

FIG. 5B is an explanation view of the conductive ball of the exemplary embodiment.

FIG. 6 is a sectional view depicting a manufacturing method of the conductive ball of the exemplary embodiment (1 thereof).

FIGS. 7A and 7B are sectional views depicting the manufacturing method of the conductive ball of the exemplary embodiment (2 thereof).

FIG. 8 is a sectional view depicting the manufacturing method of the conductive ball of the exemplary embodiment (3 thereof).

FIG. 9 is a sectional view depicting the manufacturing method of the conductive ball of the exemplary embodiment (4 thereof).

FIG. 10 is a sectional view depicting the manufacturing method of the conductive ball of the exemplary embodiment (5 thereof).

FIG. 11 is a sectional view depicting a manufacturing method of an electronic device of the exemplary embodiment (1 thereof).

FIG. 12 is a sectional view depicting the manufacturing method of the electronic device of the exemplary embodiment (2 thereof).

FIG. 13 is a sectional view depicting the manufacturing method of the electronic device of the exemplary embodiment (3 thereof).

FIG. 14 is a sectional view depicting a form of a connection part made by the conductive ball of the electronic device of the exemplary embodiment.

FIG. 15 is a sectional view depicting a test sample for checking an intermetallic compound (1 thereof).

FIG. 16 is a sectional view depicting the test sample for checking the intermetallic compound (2 thereof).

FIG. 17 depicts a relation between an area occupying ratio of a mesh pattern of a mask jig and a Cu concentration in a Sn/Ag solder.

FIG. 18 is a sectional view depicting a form of a connection part made by the conductive ball of an electronic device of a modified embodiment.

FIG. 19 is a sectional view depicting an electronic device of a first application example of the exemplary embodiment (1 thereof).

FIG. 20 is a sectional view depicting an electronic device of a second application example of the exemplary embodiment (2 thereof).

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment will be described with reference to the accompanying drawings.

Before describing the exemplary embodiment, preliminary matters, which are bases of the present disclosure, are first described. It should be noted that the preliminary matters include personal investigation contents of the inventors and include technology contents, which are not a known technology.

FIG. 1 depicts a conductive ball that is to be used for an electronic device relating to the preliminary matters. As shown in FIG. 1, in a conductive ball 100, a nickel (Ni) layer 120 and a tin (Sn)/silver (Ag) solder 130 are formed in order on an outer surface of a copper (Cu) ball 110. The Ni layer 120 functions as a barrier layer for preventing Cu of the Cu ball 110 from diffusing into the Sn/Ag solder 130.

Subsequently, a method of interconnecting a lower wiring substrate and an upper wiring substrate by using the conductive ball 100 of FIG. 1 is described. As shown in FIG. 2, a lower wiring substrate 200 that is to be arranged at a lower side of the conductive ball 100 is first prepared. A connection pad P1 is formed on an insulation layer 220 of the lower wiring substrate 200, and a solder resist layer 240 having an opening 240 a provided on the connection pad P1 is formed on the insulation layer 220.

The connection pad P1 is formed by depositing a copper (Cu) layer 260 a, a nickel (Ni) layer 260 b and a gold (Au) layer 260 c in order from below.

Also, as shown in FIG. 2, an upper wiring substrate 300 that is to be arranged at an upper side of the conductive ball 100 is prepared. In FIG. 2, the upper wiring substrate 300 is shown with being inverted upside down.

A connection pad P2 is formed on (beneath, in FIG. 2) an insulation layer 320 of the upper wiring substrate 300, and a solder resist layer 340 having an opening 340 a provided on the connection pad P2 is formed on the insulation layer 320. The connection pad P2 is formed by depositing a copper (Cu) layer 360 a, a nickel (Ni) layer 360 b and a gold (Au) layer 360 c in order from below.

Then, as shown in FIG. 3, the connection pad P1 of the lower wiring substrate 200 and the connection pad P2 of the upper wiring substrate 300 are interconnected by the conductive ball 100 of FIG. 1.

Actually, the conductive ball 100 is first arranged on the connection pad P1 of the lower wiring substrate 200, and the Sn/Ag solder 130 of the conductive ball 100 is connected to the connection pad P1 of the lower wiring substrate 200 by reflow heating.

Thereafter, the connection pad P2 of the upper wiring substrate 300 is arranged on the conductive ball 100 connected to the lower wiring substrate 200. Also, the connection pad P2 of the upper wiring substrate 300 is connected to the Sn/Ag solder 130 of the conductive ball 100 by the reflow heating.

At this time, during the reflow heating, the Au layer 260 c of the connection pad P1 of the lower wiring substrate 200 flows into the Sn/Ag solder 130 of the conductive ball 100 and is thus lost. Also, the Au layer 360 c of the connection pad P2 of the upper wiring substrate 300 flows into the Sn/Ag solder 130 of the conductive ball 100 and is thus lost.

As shown in a partially enlarged sectional view of FIG. 3, a Ni₃Sn₄ layer Ma is formed between the Ni layer 260 b of the connection pad P1 of the lower wiring substrate 200 and the Sn/Ag solder 130 of the conductive ball 100. The Ni₃Sn₄ layer Ma is an intermetallic compound in which Ni in the Ni layer 260 b of the connection pad P1 of the lower wiring substrate 200 and Sn in the Sn/Ag solder 130 of the conductive ball 100 are joined each other.

Also, a Ni₃Sn₄ layer Mb is formed between the Ni layer 360 b of the connection pad P2 of the upper wiring substrate 300 and the Sn/Ag solder 130 of the conductive ball 100. The Ni₃Sn₄ layer Mb is an intermetallic compound in which Ni in the Ni layer 360 b of the connection pad P2 of the upper wiring substrate 300 and Sn in the Sn/Ag solder 130 of the conductive ball 100 are joined each other.

Also, a Ni₃Sn₄ layer Mc is formed between the Ni layer 120 and the Sn/Ag solder 130 of the conductive ball 100. The Ni₃Sn₄ layer Mc is an intermetallic compound in which Ni in the Ni layer 120 of the conductive ball 100 and Sn in the Sn/Ag solder 130 are joined each other.

In the below, regarding problems of the electronic device of the preliminary matters, a connection part between the connection pad P1 of the lower wiring substrate 200 and the conductive ball 100 is noted.

The Ni₃Sn₄ layer Ma formed in the electronic device of the preliminary matters has a thermally unstable property. For this reason, when heat is applied during a thermal cycle test and the like, the Ni₃Sn₄ layer Ma grows, so that cracks are likely to be generated around the Ni₃Sn₄ layer Ma.

Also, the Ni₃Sn₄ layer Ma is an aggregate of acicular crystals, in which heights and widths of the respective crystals are not uniform, and has low denseness. Also, since the Ni₃Sn₄ layer Ma has low strength and is brittle, it is likely to be broken when stress is applied.

For this reason, when current is caused to flow, Ni in the Ni layer 260 b of the connection pad P1 moves from intervals of the crystals of the Ni₃Sn₄ layer Ma toward the Sn/Ag solder 130 by electromigration, so that voids are likely to be formed.

Like this, since the brittle Ni₃Sn₄ layers Ma, Mb, Mc, which are thermally unstable, are formed in the connection parts of the conductive ball 100, the connection reliability by the conductive ball 100 between the lower wiring substrate 200 and the upper wiring substrate 300 is not secured.

Subsequently, a case where the connection pads P1, P2 of the lower wiring substrate 200 and the upper wiring substrate 300 are formed of Cu layers. FIG. 4 depicts an aspect where the Sn/Ag solder 130 of the conductive ball 100 of FIG. 1 is connected to the respective connection pads P1, P2 (Cu layer) of the lower wiring substrate 200 and the upper wiring substrate 300 by reflow heating.

As shown in a partially enlarged sectional view of FIG. 4, when the connection pad P1 of the lower wiring substrate 200 is formed of the Cu layer, an intermetallic compound Mx configured by a Cu₃Sn layer Md and a Cu₆Sn₅ layer Me in order from below is formed between the connection pad P1 and the Sn/Ag solder 130 of the conductive ball 100.

Also, the same intermetallic compound Mx is formed between the connection pad P2 of the upper wiring substrate 300 and the Sn/Ag solder 130 of the conductive ball 100. Also, in the conductive ball 100, like FIG. 3, the Ni₃Sn₄ layer Mc is formed between the Ni layer 120 and the Sn/Ag solder 130.

When the Cu₆Sn₅ layer Me is formed between the connection pad P1 and the Sn/Ag solder 130, the Cu₆Sn₅ layer Me is transformed into a different crystal structure by temperature change and a volume thereof increases. Accordingly, cracks are generated around the Cu₆Sn₅ layer Me.

Like this, when the connection pad P1 is formed of the Cu layer, the unstable Cu₆Sn₅ layer Me is formed in the connection part of the conductive ball 100. For this reason, the connection reliability by the conductive ball 100 between the lower wiring substrate 200 and the upper wiring substrate 300 is not secured.

The above problems can be solved by manufacturing an electronic device with a conductive ball of an exemplary embodiment to be described later.

Exemplary Embodiment

FIG. 5A depicts a conductive ball of an exemplary embodiment, FIGS. 6 to 10 depicts a manufacturing method of the conductive ball of the exemplary embodiment.

As shown in FIG. 5A, a conductive ball 1 of the exemplary embodiment has a copper (Cu) ball 10, as a core ball. Also, a nickel (Ni) layer 12 is formed with being patterned on an outer surface of the Cu ball 10, and the outer surface of the Cu ball 10 is exposed from opening regions of the Ni layer 12.

Also, a tin (Sn)/silver (Ag) solder 14 covers each outer surface of the Cu ball 10 and the Ni layer 12. Outer surfaces of portions of the Cu ball 10 exposed from the Ni layer 12 are in contact with the Sn/Ag solder 14.

As described later, the conductive ball 1 is connected to a connection pad of an electronic member by reflow heating. At this time, Cu in the Cu ball 10 is diffused from the opening regions of the Ni layer 12 into the Sn/Ag solder 14.

At this time, an area of the Cu ball 10 exposed from the Ni layer 12 is adjusted so that Cu in the Cu ball 10 is supplied to the Sn/Ag solder 14 and thus a Cu concentration in the Sn/Ag solder 14 becomes 0.7 wt % to 3 wt %.

In a case where r_(CU-core) is radius of the Cu ball 10, T_(Ni) is thickness of the Ni layer 12, and R_(Ni) is pattern ratio of the Ni layer 12 (ratio of an area of Ni layer 12 except for the opening regions with respect to a total area of the Ni layer including the opening regions), the volume (V_(Cu-core)) of the Cu ball 10 is calculated by the following equation: V_(Cu-core)=(4π/3)×(r_(Cu-core))³, and the volume (V_(Ni)) of the Ni layer 12 is calculated by the following equation: V_(Ni)=R_(Ni)×(4π/3): [(r_(Cu-core)+T_(Ni))³−(r_(Cu-core))³].

In a case where in the Cu ball 10, Cu in an area (area “A” which is colored by grey in FIG. 5B) having a certain thickness from the surface of the Cu ball 10 exposed from the opening regions of the Ni layer 12 is considered to be diffused into the Sn/Ag solder 14 and Td_(Cu) is the thickness of the Cu in the Cu ball 10 which will be diffused into the Sn/Ag solder 14 from the opening regions of the Ni layer 12 (for example, 1-3 μm), the volume (Vd_(Cu)) of the thickness of the Cu which will be diffused into the Sn/Ag solder 14 is calculated by the following equation (1):

Vd _(Cu)=(4π/3)×[(1−R _(Ni))×(r _(Cu-core))³−(r _(Cu-core) −Td _(Cu))³]  (1)

In a case where T_(solder) is thickness of the Sn/Ag solder 14 formed on the Ni layer 12, the volume (V_(solder)) of the Sn/Ag solder 14 is calculated by the following equation (2):

V _(solder)=(4π/3)×{[(r _(Cu-core) +T _(Ni) +T _(solder))³−(r _(Cu-core) +T _(Ni))³]+(1−R _(Ni))×[(r _(Cu-core) +T _(Ni))³−(r _(Cu-core))³]}  2)

In a case where Dec_(u) is density of the Cu and D_(esolder) is density of the Sn/Ag solder 14, the Cu concentration (C_(Cu)) in the Sn/Ag solder 14 is obtained by the following equation (3):

C _(Cu)=100×[(De _(Cu) ×Vd _(Cu))/(De _(Cu) ×uVd _(Cu) +De _(solder) ×V _(solder))]  (3)

The area of the Cu ball 10 exposed from the Ni layer 12 is adjusted so that the Cu concentration calculated by the above equation (3) becomes 0.7 wt % to 3 wt %.

By the above conditions, a (Cu, Ni)₆Sn₅ layer, which is an intermetallic compound, is formed between the Ni layer 12 and the Sn/Ag solder 14 of the conductive ball 1 and between a connection pad of an electronic member and the Sn/Ag solder 14.

The (Cu, Ni)₆Sn₅ layer is an intermetallic compound in which a part of Cu in the Cu₆Sn₅ layer shown in FIG. 4 is replaced with Ni. The (Cu, Ni)₆Sn₅ layer has a thermally stable property and the crystal growth does not occur therein even when heat is applied. Also, in the (Cu, Ni)₆Sn₅ layer, the transformation of the crystal structure due to the temperature change does not occur. Also, since the (Cu, Ni)₆Sn₅ layer has high strength and denseness, it functions as a barrier layer having high reliability.

The Sn/Ag solder 14 is an example of the tin-based solder. In addition, a tin (Sn)/bismuth (Bi)solder or a tin (Sn)/bismuth (Bi)/nickel (Ni) solder may also be used.

Since the conductive ball 1 has the Cu ball 10 that is not melted during the reflow heating, it is possible to secure a predetermined interval between the lower electronic member and the upper electronic member when interconnecting the same.

Subsequently, a manufacturing method of the conductive ball 1 of the exemplary embodiment of FIG. 5A is described. As shown in FIG. 6, the Cu ball 10 is first prepared. A diameter of the Cu ball 10 is about 130 μm, for example.

Also, as shown in FIGS. 7A and 7B, a mask jig 20 having a plurality of fine openings 20 b arranged by a mesh pattern 20 a is prepared. The mask jig 20 is formed of a fluorine resin, for example. A size of the opening 20 b of the mask jig 20 is set smaller than a size of the copper ball 10. FIG. 7B is a sectional view taken along a line I-I of FIG. 7A.

Continuously, as shown in FIG. 8, the Cu balls 10 of FIG. 6 are sandwiched from upper and lower sides by the two mask jigs 20, and the entire outer surfaces of the Cu balls 10 are wrapped by the mask jigs 20. At this time, portions of the outer surfaces of the Cu balls 10 are exposed from the plurality of openings 20 b of the mask jigs 20.

Then, the plurality of Cu balls 10 sandwiched by the mask jigs 20 are immersed in a plating solution 24 introduced into a plating bath 22 of an electroless plating device.

Then, as shown in FIG. 9, the outer surfaces of the Cu balls 10 are subjected to an electroless plating through the openings 20 b of the mask jigs 20, so that the Ni layers 12 are formed with being patterned. The outer surfaces of portions, which correspond to the openings 20 b of the mask jigs 20, of the Cu balls 10 are formed with the Ni layers 12.

On the other hand, the outer surfaces of portions, which correspond to the mesh patterns 20 a of the mask jigs 20, of the Cu balls 10 are not formed with the Ni layer 12, and portions of the outer surfaces of the Cu balls 10 are thus exposed from the Ni layer 12.

The electroless plating for forming the Ni layer 12 is performed on the basis of following conditions, for example. First, the Cu ball 10 is immersed in a mixed solution (room temperature) of caustic soda:10 g/L and surfactant 0.5 g/L for one minute for degreasing. Continuously, the Cu ball 10 is immersed in a sulfuric acid solution (room temperature) for one minute for acid cleaning.

Then, the Cu ball 10 is treated with a mixed solution (room temperature) of palladium chloride:2 g/L, sodium chloride:200 g/L, and 35% HCl solution:30 ml for 5 minutes. Thereby, Pd is applied to the outer surface of the Cu ball 10, as catalyst.

Thereafter, the Cu ball 10 is treated with an electroless plating solution (90° C.) including nickel sulfate:20 g/L and sodium hypophosphite:24 g/L for 15 minutes. Thereby, a Ni (P) layer of phosphorous (P) 10 wt % having a thickness of about 2 μm is formed as the Ni layer 12.

In this way, the Ni layers 12 are formed with being patterned on the outer surfaces of the Cu balls 10 by the electroless plating in the state where the Cu balls 10 are sandwiched by the mask jigs 20 having the plurality of openings 20 b. Thereby, the outer surfaces of the Cu balls 10 are exposed from the opening regions of the Ni layers 12.

Then, the Cu balls 10 having the Ni layers 12 formed thereon are detached from the mask jigs 20. Then, as shown in FIG. 10, the Cu balls 10 having the Ni layers 12 formed thereon are immersed in a plating solution 24 a introduced into a plating bath 22 a of an electrolytic plating device. Then, a Sn/Ag solder 14 covering the outer surfaces of the Cu ball 10 and the Ni layer 12 is formed by an electrolytic plating.

The electrolytic plating of the Sn/Ag solder 14 is performed by the barrel plating. As conditions of the electrolytic plating, an electrolytic Sn/Ag plating solution (UTB TS-140 (ISHIHARA CHEMICAL CO., LTD)) is used, a current denseness is set to 3 A/dm², and treatment is performed at room temperature for 9 minutes. Thereby, the Sn/Ag solder 14 having a thickness of about 12 μm is formed.

In addition to the Sn/Ag solder 14, a Sn/Bi solder or a Sn/Bi/the Ni solder may also be formed.

By the above processes, the conductive ball 1 of FIG. 5A is manufactured.

In the embodiment, the mask jig 20 having the plurality of fine openings 20 b arranged by the mesh pattern 20 a is used. However, a mask jig having a plurality of fine circular openings can be used so that a Ni layer having a plurality of circular opening regions can be formed.

Subsequently, a method of manufacturing an electronic device by using the conductive ball 1 of FIG. 5A is described with reference to FIGS. 11 to 14.

As shown in FIG. 11, a lower electronic member 5 is first prepared. FIG. 11 partially depicts a surrounding aspect of a connection pad P1 of the lower electronic member 5. The lower electronic member 5 is a mounting substrate such as a wiring substrate, a motherboard and the like, for example.

As shown in FIG. 11, the lower electronic member 5 is formed with the connection pad P1 on an insulation layer 30. Also, a solder resist layer 32 having an opening 32 x provided on the connection pad P1 is formed on the insulation layer 30.

The connection pad P1 is formed by depositing a copper (Cu) layer 40, a nickel (Ni) layer 42 and a gold (Au) layer 44 in order from below. The opening 32 x of the solder resist layer 32 is arranged on the pad-shaped Cu layer 40, and an outer peripheral part of the Cu layer 40 is covered with the solder resist layer 32. The Ni layer 42 and the Au layer 44 are formed on the Cu layer 40 in the opening 32 x of the solder resist layer 32 by a plating.

The Cu layer 40 may be a pad electrode arranged in an island form or may be a pad electrode coupled to a leading wiring. The connection pad P1 is connected to an internal wiring layer through a via conductor formed in the insulation layer 30.

Then, the conductive ball 1 of FIG. 5A is arranged on the connection pad P1 of the lower electronic member 5. Also, as shown in FIG. 12, the reflow heating is performed to melt the Sn/Ag solder 14 of the conductive ball 1, so that the conductive ball 1 is connected to the connection pad P1 of the lower electronic member 5 by the Sn/Ag solder 14. At this time, the Sn/Ag solder 14 is reflow-heated to a temperature of 240′C to 260° C.

By the reflow heating, the Au layer 44 of the connection pad P1 of the lower electronic member 5 is caused to flow into the Sn/Ag solder 14 and is thus lost.

A (Cu, Ni)₆Sn₅ layer M1 is formed between the connection pad P1 of the lower electronic member 5 and the Sn/Ag solder 14 of the conductive ball 1.

During the reflow heating, Cu in the Cu ball 10 of the conductive ball 1 is diffused and supplied to the Sn/Ag solder 14 through the opening regions of the Ni layer 12. Thereby, Cu, Ni in the Ni layer 42 of the connection pad P1 and Sn in the Sn/Ag solder 14 are joined one another, so that a (Cu, Ni)₆Sn₅ layer M1 is formed.

Also, as shown in a partially enlarged sectional view of FIG. 12, a (Cu, Ni)₆Sn₅ layer M2 is formed between the Ni layer 12 and the Sn/Ag solder 14 of the conductive ball 1. During the reflow heating, Cu in the Cu ball 10 of the conductive ball 1 is diffused and supplied to the Sn/Ag solder 14 through the opening regions of the Ni layer 12.

Thereby, Cu, Ni in the Ni layer 12 of the conductive ball 1 and Sn in the Sn/Ag solder 14 are joined one another, so that the (Cu, Ni)Sn₅ layer M2 is formed.

Also, likewise, as shown in the partially enlarged sectional view of FIG. 12, a Cu₃Sn layer My is formed on the outer surface of the Cu ball 10 exposed from the Ni layer 12 of the conductive ball 1. Cu in the Cu ball 10 and Sn in the Sn/Ag solder 14 are joined each other, so that the Cu₃Sn layer My is formed.

Also, a (Cu, Ni)₆Sn₅ layer M3 is formed between the Cu₃Sn layer My formed on the outer surface of the Cu ball 10 and the Sn/Ag solder 14. Cu in the Cu ball 10 of the conductive ball 1 and Ni in the Ni layer 12 are supplied to the Sn/Ag solder 14, so that Cu, Ni and Sn are joined one another and the (Cu, Ni)₆Sn₅ layer M3 is thus formed on the Cu₃Sn layer My.

In this way, the (Cu, Ni)₆Sn₅ layer M2 is formed on the Ni layer 12 patterned on the outer surface of the Cu ball 10 of the conductive ball 1. At the same time, the Cu₃Sn layer My and the (Cu, Ni)₆Sn₅ layer M3 are formed in order from below on the outer surface of the Cu ball 10 exposed from the Ni layer 12.

Thereby, the entire outer surface of the Cu ball 10 of the conductive ball 1 is covered with the (Cu, Ni)₆Sn₅ layers M2, M3.

Then, as shown in FIG. 13, an upper electronic member 6 that is to be arranged at an upper side of the conductive ball 1 is prepared. The upper electronic member 6 is an electronic component such as a wiring substrate, a semiconductor chip or the like, for example. In FIG. 13, the upper electronic member 6 is shown with being inverted upside down.

In the upper electronic member 6, a connection pad P2 is formed on (beneath, in FIG. 13) an insulation layer 30 a, and a solder resist layer 32 a having an opening 32 x provided on the connection pad P2 is formed on the insulation layer 30 a. The connection pad P2 is formed by depositing a copper (Cu) layer 40 a, a nickel (Ni) layer 42 a and a gold (Au) layer 44 a in order from below.

Then, the connection pad P2 of the upper electronic member 6 is arranged on the conductive ball 1 connected to the connection pad P1 of the lower electronic member 5.

Continuously, as shown in FIG. 14, the reflow heating is performed to melt the Sn/Ag solder 14 of the conductive ball 1, so that the connection pad P2 of the upper electronic member 6 is connected to the Sn/Ag solder 14 of the conductive ball 1.

At this time, like the lower electronic member 5, the Au layer 44 a of the connection pad P2 of the upper electronic member 6 is caused to flow into the Sn/Ag solder 14 and is thus lost by the reflow heating.

Then, like the lower electronic member 5, a (Cu, Ni)₆Sn₅ layer M4 is formed between the Ni layer 42 a of the connection pad P2 of the upper electronic member 6 and the Sn/Ag solder 14.

Like the lower electronic member 5, during the reflow heating, Cu in the Cu ball 10 of the conductive ball 1 is supplied to the Sn/Ag solder 14 through the opening regions of Ni layer 12. Thereby, Cu, Ni in the Ni layer 42 a of the connection pad P2 and Sn in the Sn/Ag solder 14 are joined, so that the (Cu, Ni)₆Sn₅ layer M4 is formed.

In this way, the connection pad P1 of the lower electronic member 5 is connected to the connection pad P2 of the upper electronic member 6 by the conductive ball 1. Since the Cu ball 10 of the conductive ball 1 is not melted when reflow heating the Sn/Ag solder 14, it is possible to secure a predetermined interval between the lower electronic member 5 and the upper electronic member 6.

In the above example, after connecting the conductive ball 1 to the first connection pad P1 of the lower electronic member 5, the connection pad P2 of the upper electronic member 6 is connected to the conductive ball 1. To the contrary, after connecting the conductive ball 1 to the connection pad P2 of the upper electronic member 6, the connection pad P1 of the lower electronic member 5 may be connected to the conductive ball 1.

Alternatively, in a state where the conductive ball 1 is arranged between the connection pad P1 of the lower electronic member 5 and the connection pad P2 of the upper electronic member 6, both may be connected at the same time by collectively performing the reflow heating.

In this way, the connection pad P1 of the lower electronic member 5 and the connection pad P2 of the upper electronic member 6 are connected by reflow heating the tin-based solder 14 of the conductive ball 1.

By the above processes, as shown in FIG. 14, an electronic device 2 of the exemplary embodiment is obtained. As shown in FIG. 14, the electronic device 2 of the exemplary embodiment has the lower electronic member 5. In the lower electronic member 5, the connection pad P1 is formed on the insulation layer 30. Also, the solder resist layer 32 having the opening 32 x provided on the connection pad P1 is formed on the insulation layer 30.

The connection pad P1 is formed by the Cu layer 40 and the Ni layer 42 arranged thereon. A surface of the connection pad P1 is formed as the Ni layer 42.

The opening 32 x of the solder resist layer 32 is arranged on the pad-shaped Cu layer 40, and an outer peripheral part of the Cu layer 40 is covered thereon with the solder resist layer 32. The Ni layer 42 is formed on the Cu layer 40 in the opening 32 x of the solder resist layer 32.

Also, the conductive ball 1 is connected to the connection pad P1 of the lower electronic member 5. The conductive ball 1 has the Cu ball 10, the Ni layer 12 formed with being patterned on the outer surface of the Cu ball 10 and the Sn/Ag solder 14 covering each outer surface of the Cu ball 10 and the Ni layer 12.

The (Cu, Ni)₆Sn₅ layer M1 is formed between the Ni layer 42 of the connection pad P1 of the lower electronic member 5 and the Sn/Ag solder 14 of the conductive ball 1. As described above, the (Cu, Ni)₆Sn₅ layer M1 is an intermetallic compound in which Cu supplied from the Cu ball 10 of the conductive ball 1, Ni in the Ni layer 42 of the connection pad P1 and Sn in the Sn/Ag solder 14 are joined one another.

Also, the electronic device 2 of the exemplary embodiment has the upper electronic member 6 arranged above the lower electronic member 5. The conductive ball 1 is arranged between the connection pad P1 of the lower electronic member 5 and the connection pad P2 of the upper electronic member 6, and the connection pad P1 and the second connection pad P2 are interconnected by the conductive ball 1.

In this way, the lower electronic member 5 is connected to the upper electronic member 6 by the conductive ball 1. The upper electronic member 6 is inverted upside down.

In the upper electronic member 6, the connection pad P2 is formed on (beneath, in FIG. 14) the insulation layer 30 a. Also, the solder resist layer 32 a having the opening 32 x provided on the connection pad P2 is formed on the insulation layer 30 a.

Like the lower electronic member 5, the connection pad P2 is formed by the Cu layer 40 a and the Ni layer 42 a arranged thereon. The opening 32 x of the solder resist layer 32 a is arranged on the pad-shaped Cu layer 40 a, and an outer peripheral part of the Cu layer 40 a is covered thereon with the solder resist layer 32 a. The Ni layer 42 a is formed on the Cu layer 40 a in the opening 32 x of the solder resist layer 32 a.

Also, like the lower electronic member 5, the (Cu, Ni)₆Sn₅ layer M4 is formed between the Ni layer 42 a of the connection pad P2 of the upper electronic member 6 and the Sn/Ag solder 14 of the conductive ball 1. Like the lower electronic member 5, the (Cu, Ni)₆Sn₅ layer M4 is an intermetallic compound in which Cu supplied from the Cu ball 10 of the conductive ball 1, Ni in the Ni layer 42 a of the connection pad P2 and Sn in the Sn/Ag solder 14 are joined one another.

Like this, in the electronic device 2 of the exemplary embodiment, the (Cu, Ni)₆Sn₅ layer M1, which is an intermetallic compound, is formed between the Ni layer 42 of the connection pad P1 of the lower electronic member 5 and the Sn/Ag solder 14 of the conductive ball 1.

The (Cu, Ni)₆Sn₅ layer M1 has a thermally stable property, unlike the Ni₃Sn₄ layer Ma described in the preliminary matters. For this reason, even when heat is applied during a thermal cycle test and the like, the crystal growth does not occur.

Also, in the (Cu, Ni)₆Sn₅ layer M1, the transformation of the crystal structure due to the temperature change does not occur, unlike the Cu₆Sn₅ layer Me described in the preliminary matters. For this reason, the cracks are prevented from being generated around the (Cu, Ni)₆Sn₅ layer M1.

Also, the (Cu, Ni)₆Sn₅ layer M1 is an aggregate of dome-shaped crystals, in which heights and widths of the respective crystals are uniform, and has high denseness, unlike the Ni₃Sn₄ layer Ma described in the preliminary matters. Also, the (Cu, Ni)₆Sn₅ layer M1 has high strength, so that it is difficult to be broken even when stress is applied thereto.

For this reason, since the (Cu, Ni)₆Sn₅ layer M1 functions as a barrier layer having high reliability, Ni in the Ni layer 42 of the connection pad P1 of the lower electronic member 5 is suppressed from moving by the electromigration, so that a void is prevented from being generated in the connection part made by the conductive ball 1.

Also, the (Cu, Ni)₆Sn₅ layer M4 is formed between the Ni layer 42 a of the connection pad P2 of the upper electronic member 6 and the Sn/Ag solder 14 of the conductive ball 1. For this reason, due to the similar reasons, it is possible to improve the connection reliability between the connection pad P2 of the upper electronic member 6 and the conductive ball 1.

Also, referring to a partially enlarged sectional view of FIG. 14, the (Cu, Ni)₆Sn₅ layer M2 is formed between the Ni layer 12 and the Sn/Ag solder 14 of the conductive ball 1. As described above, the (Cu, Ni)₆Sn₅ layer M2 is an intermetallic compound in which Cu supplied from the Cu ball 10, Ni in the Ni layer 12 and Sn in the Sn/Ag solder 14 in the conductive ball 1 are joined one another.

Also, as shown in a partially enlarged sectional view of FIG. 14, the Cu₃Sn layer My is formed on the outer surface of the Cu ball 10 exposed from the Ni layer 12 of the conductive ball 1. The Cu₃Sn layer My is an intermetallic compound in which Cu in the Cu ball 10 and Sn in the Sn/Ag solder 14 are joined each other.

Also, the (Cu, Ni)₆Sn₅ layer M3 is formed between the Cu₃Sn layer My formed on the outer surface of the Cu ball 10 and the Sn/Ag solder 14. As described above, the (Cu, Ni)₆Sn₅ layer M3 is an intermetallic compound in which Cu in the Cu ball 10 of the conductive ball 1 and Ni in the Ni layer 12 are diffused into the Sn/Ag solder 14 and Cu, Ni and Sn are thus joined one another.

In this way, the entire outer surface of the Cu ball 10 of the conductive ball 1 is covered with the (Cu, Ni)₆Sn₅ layers M2, M3.

Thereby, also in the (Cu, Ni)₆Sn₅ layers M2, M3 formed in the conductive ball 1, since the crystal growth and the transformation do not occur, as described above, the crack is prevented from being generated in the connection part made by the conductive ball 1.

Also, Ni in the Ni layer 12 of the conductive ball 1 is suppressed from moving by the electromigration, so that a void is prevented from being generated in the connection part made by the conductive ball 1.

Also, even when Ni layer 12 is patterned on the outer surface of the Cu ball 10 of the conductive ball 1, Cu in the Cu ball 10 is prevented from being diffused into the Sn/Ag solder 14 by the (Cu, Ni)₆Sn₅ layers M2, M3.

Here, conditions at which the (Cu, Ni)₆Sn₅ layers M1 to M4 are formed on the Ni layers 42, 42 a of the connection pads P1, P2 of the lower electronic member 5 and the upper electronic member 6 and on the Ni layer 12 of the conductive ball 1 are described.

When reflow heating the conductive ball 1 for connection, Cu in the Cu ball 10 of the conductive ball 1 is diffused into the Sn/Ag solder 14 from the opening regions of Ni layer 12. At this time, the Cu concentration in the Sn/Ag solder 14 is adjusted to be within a range of 0.7 wt %/o to 3 wt %, so that the (Cu, Ni)₆Sn₅ layers M1 to M4 are formed.

The inventors performed a test for checking whether the (Cu, Ni)₆Sn₅ layer is actually formed by the above conditions.

As shown in FIG. 15, as a test sample, a lower substrate 5 a and an upper substrate 6 a were prepared. In the lower substrate 5 a, a pad-shaped Cu layer 40 b was formed on an insulation layer 30 b, and a solder resist layer 32 b having an opening 32 x provided on the Cu layer 40 b was formed.

Also, a Ni layer 42 b, a Pd layer 43 b and an Au layer 44 b were formed on the Cu layer 40 b in the opening 32 x of the solder resist layer 32. A connection pad Px was formed by the Cu layer 40 b, the Ni layer 42 b, the Pd layer 43 b and the Au layer 44 b. Also, in the upper substrate 6 a, a Cu pillar 48 was formed on an insulation layer 30 c.

Then, a solder paste 49 a of 96 wt % Sn/3.5 wt % Ag/0.5 wt % Cu was applied onto the connection pad Px of the lower substrate 5 a.

The test sample is a pseudo test of the connection structure of FIG. 14, and the Cu pillar 48 of the upper substrate 6 a corresponds to the Cu ball 10 of the conductive ball 1 and the solder paste 49 a corresponds to the Sn/Ag solder 14 of the conductive ball 1.

Then, as shown in FIG. 16, the Cu pillar 48 of the upper substrate 6 a was arranged on the solder paste 49 a on the connection pad Px of the lower substrate 5 a, and the reflow heating was performed. Thereby, the Cu pillar 48 of the upper substrate 6 a was connected to the connection pad Px of the lower substrate 5 a by a solder 49.

At this time, the Au layer 44 b and Pd layer 43 b of the connection pad Px flowed into the solder paste 49 a and were thus lost. Also, Cu in the Cu pillar 48 was diffused into the solder paste 49 a, so that the Cu concentration in the solder paste 49 a was increased from 0.5 wt % to 0.7 wt %.

Thereby, a (Cu, Ni)₆Sn₅ layer M1 was formed between the Ni layer 42 b of the connection pad Px of the lower substrate 5 a and the solder 49.

The inventors analyzed the layer denoted with M1 in FIG. 16 by EDX (energy dispersive X-ray analysis) and confirmed that the layer denoted with M1 was the (Cu, Ni)₆Sn₅ layer.

Like this, it was confirmed that the (Cu, Ni)₆Sn₅ layer was formed by adjusting the Cu concentration in the Sn/Ag solder 14 to a range of 0.7 wt % to 3 wt % by the diffusion of Cu from the Cu ball 10 of the conductive ball 1.

FIG. 17 depicts a relation between an area occupying ratio (%) of the mesh pattern 20 a of the mask jig 20 shown in FIGS. 7A and 7B and the Cu concentration (wt %) in the Sn/Ag solder. The area occupying ratio (%) of the mesh pattern 20 a of the mask jig 20 is a ratio of a total area of the mesh pattern 20 a to a total area of the mask jig 20.

The mesh pattern 20 a of the mask jig 20 corresponds to the portions of the outer surface of the Cu ball 10 exposed from the Ni layer 12.

For example, like the conductive ball 1 of FIG. 17, the Ni layer 12 having a thickness of 2 μm is formed with being patterned on the outer surface of the Cu ball 10 having a diameter of 130 μm, and the Sn/Ag solder 14 having a thickness of 13 μm is further formed, so that an entire diameter is set to 160 μm.

During the reflow heating, it is assumed that Cu corresponding to a thickness of about 2 μm is diffused from the Cu ball 10 into the Sn/Ag solder 14.

In this case, as shown in a graph of FIG. 17, when the area occupying ratio (%) of the mesh pattern 20 a is set to 6%, the Cu concentration in the Sn/Ag solder 14 is 0.7 wt %. Also, when the area occupying ratio (%) of the mesh pattern 20 a is set to 10%, the Cu concentration in the Sn/Ag solder 14 is 1.16 wt %.

Actually, since it is possible to increase a diffusion amount of Cu by prolonging a time period of the reflow heating, it doesn't matter even if the area occupying ratio (%) of the mesh pattern 20 a is 6% or less.

Like this example, the area of the copper ball 10 exposed from the Ni layer 12 is preferably adjusted so that Cu in the Cu ball 10 is diffused into the Sn/Ag solder 14 and the Cu concentration in the Sn/Ag solder 14 becomes 0.7 wt % to 3 wt % during the reflow heating.

Subsequently, an electronic device of a modified embodiment of the exemplary embodiment is described. FIG. 18 depicts an electronic device of a modified embodiment of the exemplary embodiment. As shown in FIG. 18, in an electronic device 2 a of the modified embodiment, the respective connection pads P1, P2 of the lower electronic member 5 and the upper electronic member 6 are formed of the Cu layers without the Ni layer and the Au layer.

FIG. 18 depicts an aspect in which the Sn/Ag solder 14 of the conductive ball 1 of FIG. 5A is connected to the respective connection pads P1, P2 (Cu layers) of the lower electronic member 5 and the upper electronic member 6 by the reflow heating.

As shown in FIG. 18, in the electronic device 2 a of the modified embodiment, a Cu₃Sn layer My and a (Cu, Ni)₆Sn₅ layer M5 are formed in order from below between the connection pad P1 (Cu layer) of the lower electronic member 5 and the Sn/Ag solder 14 of the conductive ball 1. Cu in the connection pad P1 (Cu layer) of the lower electronic member 5 and Sn in the Sn/Ag solder 14 are joined each other, so that the Cu₃Sn layer My is formed on the connection pad P1.

Also, at the same time, Cu in the Cu ball 10 of the conductive ball 1 and Ni in the Ni layer 12 are diffused into the Sn/Ag solder 14, so that Cu, Ni and Sn are joined one another and the (Cu, Ni)₆Sn₅ layer M5 is thus formed on the Cu₃Sn layer My on the connection pad P1.

Also, a Cu₃Sn layer My and a (Cu, Ni)₆Sn₅ layer M6 are formed in order from below between the connection pad P2 (Cu layer) of the upper electronic member 6 and the Sn/Ag solder 14 of the conductive ball 1.

Cu in the connection pad P2 (Cu layer) of the upper electronic member 6 and Sn in the Sn/Ag solder 14 of the conductive ball 1 are joined each other, so that the Cu₃Sn layer My is formed on the connection pad P2.

Also, at the same time, Cu in the Cu ball 10 of the conductive ball 1 and Ni in the Ni layer 12 are diffused into the Sn/Ag solder 14, so that Cu, Ni and Sn are joined one another and the (Cu, Ni)₆Sn₅ layer M6 is thus formed on the Cu₃Sn layer My on the connection pad P2.

FIG. 18 is the same as FIG. 14, except that the Cu₃Sn layer My and the (Cu, Ni)₆Sn₅ layers M5, M6 are formed on the respective connection pads P1, P2 (Cu layer) of the lower electronic member 5 and the upper electronic member 6. For this reason, the other elements of FIG. 18 are denoted with the same reference numerals as FIG. 14, and the detailed descriptions thereof are omitted.

In the electronic device 2 a of the modified embodiment, since the respective connection pads P1, P2 of the lower electronic member 5 and the upper electronic member 6 do not have the Ni layer, Ni is supplied from the Ni layer 12 of the conductive ball 1, so that the (Cu, Ni)₆Sn₅ layers M5, M6 are formed.

For this reason, in the electronic device 2 a of the modified embodiment, since the supply amount of Ni from the conductive ball 1 is increased, the occupying area and thickness of the Ni layer 12 of the conductive ball 1 are largely set.

In the electronic device 2 a of the modified embodiment, like the electronic device 1 of FIG. 14, the thermally stable (Cu, Ni)₆Sn₅ layers M5, M6 are formed between the connection pads P1, P2 (Cu layer) and the Sn/Ag solder 14 and between the Ni layer 12 and the Sn/Ag solder 14 of the conductive ball 1.

For this reason, it is possible to improve the connection reliability by the conductive ball 1 between the lower electronic member 5 and the upper electronic member 6.

In FIGS. 14 and 18, even when a Sn/Bi solder or a Sn/Bi/Ni solder is used instead of the Sn/Ag solder 14 of the conductive ball 1, the similar intermetallic compound is formed.

Subsequently, an electronic device of the exemplary embodiment to which the connection structure by the conductive ball of FIG. 14 is applied is described.

FIG. 19 depicts an electronic device of a first application example of the exemplary embodiment. As shown in FIG. 19, an electronic device 3 of the first application example of the exemplary embodiment has a mounting substrate 50 such as a motherboard at a lower side.

The connection pads P1 are formed on an upper surface of the mounting substrate 50, and a wiring layer 52 is formed on a lower surface. The wiring layer 52 provided on the lower surface is covered with an insulation layer 54. Also, the mounting substrate 50 is formed with an insulation layer 56 having openings 56 a provided on the connection pads P1 on the upper surface. The mounting substrate 50 is an example of the lower electronic member.

The Sn/Ag solders 14 of the conductive balls 1 are connected to the connection pads P1 provided on the upper surface of the mounting substrate 50.

Also, a wiring substrate 60 is arranged above the mounting substrate 50 via the conductive balls 1. The wiring substrate 60 has the connection pads P2 provided on both surfaces thereof, and the connection pads P2 provided on both the surfaces are interconnected via through-conductors 62.

The wiring substrate 60 is formed with solder resist layers 64 having openings 64 a provided on the connection pads P2 on both the surfaces, respectively. The wiring substrate 60 is an example of the upper electronic member or the lower electronic member.

The connection pads P2 provided on the lower surface of the wiring substrate 60 are connected to the Sn/Ag solders 14 of the conductive balls 1.

The connection structure by the conductive ball 1 shown in FIG. 14 or 18 is applied to a structure where the connection pad P1 of the mounting substrate 50 and the connection pad P2 provided on the lower surface of the wiring substrate 60 are interconnected by the conductive ball 1.

Also, the Sn/Ag solders 14 of the conductive balls 1 are connected to the connection pads P2 provided on the upper surface of the wiring substrate 60. Also, connection pads P3 of a semiconductor chip 70 are connected to the Sn/Ag solders 14 of the conductive balls 1 connected to the wiring substrate 60. Also, an underfill resin 72 is filled at a lower side of the semiconductor chip 70. The semiconductor chip 70 is an example of the upper electronic member.

The connection structure by the conductive ball 1 shown in FIG. 14 or 18 is applied to a structure where the connection pad P2 of the wiring substrate 60 and the connection pad P3 of the semiconductor chip 70 are interconnected by the conductive ball 1.

FIG. 20 depicts an electronic device of a second application example of the exemplary embodiment. As shown in FIG. 20, in an electronic device 3 a of the second application example of the exemplary embodiment, a lower wiring substrate 60 a having the same structure as the wiring substrate 60 of FIG. 19 is arranged at a lower side.

The semiconductor chip 70 is flip chip-connected to the connection pads P2 provided on an upper surface of the lower wiring substrate 60 a by solder bumps 74. The underfill resin 72 is filled on a lower surface-side of the semiconductor chip 70. The lower wiring substrate 60 a is an example of the lower electronic member.

Also, the Sn/Ag solders 14 of the conductive balls 1 are connected to the connection pads P2 provided on the upper surface of the lower wiring substrate 60 a.

Also, an upper wiring substrate 80 is arranged above the lower wiring substrate 60 a via the conductive balls 1. Connection pads P4 are formed on both surfaces of the upper wiring substrate 80, and the connection pads P4 provided on both the surfaces are interconnected via through-conductors 82.

The upper wiring substrate 80 is formed with solder resist layers 84 having openings 84 a provided on the connection pads P4 provided on both the surfaces, respectively.

The connection pads P4 provided on the lower surface of the upper wiring substrate 80 are connected to the Sn/Ag solders 14 of the conductive balls 1. The upper wiring substrate 80 is an example of the upper electronic member. Also, a seal resin 90 is filled between the lower wiring substrate 60 a and the upper wiring substrate 80. By the seal resin 90, the semiconductor chip 70 and the conductive balls 1 are sealed.

The connection structure by the conductive ball 1 shown in FIG. 14 or 18 is applied to a structure where the connection pad P2 provided on the upper surface of the lower wiring substrate 60 a and the connection pad P4 provided on the lower surface of the upper wiring substrate 80 are interconnected by the conductive ball 1.

This disclosure further encompasses various exemplary embodiments, for example, described below.

1. A manufacturing method of a conductive ball, the manufacturing method comprising:

preparing a copper ball;

patterning and forming a nickel layer on an outer surface of the copper ball; and forming a tin-based solder covering each outer surface of the copper ball and the nickel layer.

2. A manufacturing method of an electronic device, the manufacturing method comprising:

preparing a lower electronic member an upper electronic member and a conductive ball, the lower electronic member having a first connection pad, the upper electronic member having a second connection pad, the conductive ball comprising a copper ball, a nickel layer formed with being patterned on an outer surface of the copper ball, and a tin-based solder covering each outer surface of the copper ball and the nickel layer; and

interconnecting the first connection pad of the lower electronic member and the second connection pad of the upper electronic member by reflow heating the tin-based solder of the conductive ball.

3. The manufacturing method of an electronic device according to claim 2, wherein in the preparation of the conductive ball, an area of the copper ball exposed from the nickel layer is adjusted so that copper in the copper ball is diffused into the tin-based solder and a copper concentration in the tin-based solder becomes 0.7 wt % to 3 wt % when reflow heating the tin-based solder.

4. The manufacturing method of an electronic device according to claim 3, wherein in the interconnection of the first connection pad of the lower electronic member and the second connection pad of the upper electronic member, a (Cu, Ni)₆Sn₅ layer is formed between the nickel layer and the tin-based solder of the conductive ball, and a Cu₃Sn layer and a (Cu, Ni)₆Sn₅ layer are formed in order from below between the copper ball exposed from the nickel layer of the conductive ball and the tin-based solder.

5. The manufacturing method of an electronic device according to claim 3 or 4, wherein in the interconnection of the first connection pad of the lower electronic member and the second connection pad of the upper electronic member, each surface of the first connection pad and the second connection pad is a nickel layer or a copper layer, and the (Cu, Ni)₆Sn₅ layer is respectively formed between the first connection pad and the tin-based solder and between the second connection pad and the tin-based solder. 

What is claimed is:
 1. A conductive ball comprising: a copper ball; a nickel layer formed with being patterned on an outer surface of the copper ball; and a tin-based solder covering each outer surface of the copper ball and the nickel layer.
 2. The conductive ball according to claim 1, wherein an area of the copper ball exposed from the nickel layer is adjusted so that copper in the copper ball is diffused into the tin-based solder and a copper concentration in the tin-based solder becomes 0.7 wt % to 3 wt % when reflow heating the tin-based solder.
 3. The conductive ball according to claim 1, wherein the nickel layer has at least one opening region and the outer surface of the copper ball is exposed from the opening region of the nickel layer.
 4. An electronic device comprising: a lower electronic member having a first connection pad; an upper electronic member arranged above the lower electronic member and having a second connection pad; and a conductive ball configured to interconnect the first connection pad of the lower electronic member and the second connection pad of the upper electronic member, wherein the conductive ball comprises: a copper ball, a nickel layer formed with being patterned on an outer surface of the copper ball, and a tin-based solder covering each outer surface of the copper ball and the nickel layer.
 5. The electronic device according to claim 4, wherein a (Cu, Ni)₆Sn₅ layer is formed between the nickel layer and the tin-based solder (14) of the conductive ball, and wherein a Cu₃Sn layer and a (Cu, Ni)₆Sn₅ layer are formed in order from below between the copper ball exposed from the nickel layer of the conductive ball and the tin-based solder.
 6. The electronic device according to claim 4, wherein each surface of the first connection pad and the second connection pad is a nickel layer or a copper layer, and wherein the (Cu, Ni)₆Sn₅ layer is respectively formed between the first connection pad and the tin-based solder and between the second connection pad and the tin-based solder.
 7. The electronic device according to claim 5, wherein each surface of the first connection pad and the second connection pad is a nickel layer or a copper layer, and wherein the (Cu, Ni)₆Sn₅ layer is respectively formed between the first connection pad and the tin-based solder and between the second connection pad and the tin-based solder. 